Cns 9

The Cerebellum

• The cerebellum is located dorsal to the pons and medulla under the occipital lobe of the cerebral hemispheres

Cerebellum

The Cerebellum• It is separated from

the occipital lobe by the transverse fissure

• It rests in the posterior cranial fossa of the skull

Cerebellum: Gross Anatomy•It consists of cerebellar cortex and and deep cerebellar nuclei, with white medulla in between

•Cerebellum is uninterrupted across the midline

•The cortex consists of ridges called folia.

•The cerebellum consists of three parts:

•A small inferior part …Flocculonodular lobe (floccular, means a tuft of wool);

•A narrow central vermis (worm shaped)

•Two large lateral hemispheres

nodulus

flocculus

tonsil

Ventral View

Anatomy of the CerebellumAnatomy of the Cerebellum2 symmetrical hemispheres connected medially by the Vermis

Folia: Transversely oriented gyri

3 lobes in each hemisphere: Anterior, Posterior, Flocculonodular (FN)

Neural arrangement: Gray matter (Cortex), White matter (Internal), Scattered cerebellar nuclei: dentate, globose, emboliform, fastigial

Arbor vitae (tree of life): distinctive treelike pattern of the white matter

FoliumFolium

Divisions of the Cerebellum

nodulus

flocculus

Ant LobeAnt Lobe

Ant LobeAnt Lobe

Post LobePost Lobe Post LobePost Lobetonsil

Ventral View Superior Surface

Ant Lobe

Post Lobe

nodulusflocculus

Schematic

vermis

hemisphere

CerebellumCerebellum

Regulation of muscle tone,coordination of skilled voluntary movement

Planning of voluntary activity

Maintenance of balance, control of eye movements

Vestibulocerebellum

Spinocerebellum

Cerebrocerebelum

Anterior Lobe

Posterior Lobe

Flocculo-Nodular Lobe (FN lobe)

Folia

Primary fissure

Cerebellar Subdivisions

•Multiple nomenclatures have been used to describe the various lobules

•Larsell (1952) used Roman Numerals I-X (anterior to posterior)

Archicerebellum-vestibulocerebellum

Paleocerebellum-spinocerebellum

Neocerebellum-pontocerebellum/cerebrocerebellum

Cerebellar Peduncles

MedullaInferior(ICP)

PonsMiddle(MCP)

MidbrainSuperior(SCP)

Connectsto

Peduncle

SCPSCP

SCPSCP SCPSCP

MCPMCP

MCPMCP

MCPMCP

ICPICP

ICPICP

ICPICP

The Macroscopic Anatomy of the Cerebellum

• Gross anatomical divisions– Anterior lobe– Posterior lobe– Flocculonodular lobe

The Evolutionary & Functional Division of the Cerebellum

• The cerebellum can be divided by – Evolutionary age – Function

Cerebellar Subdivisions

•Multiple nomenclatures have been used to describe the various lobules

•Larsell (1952) used Roman Numerals I-X (anterior to posterior)

Archicerebellum-vestibulocerebellum

Paleocerebellum-spinocerebellum

Neocerebellum-pontocerebellum/cerebrocerebellum

The Evolutionary Division of the Cerebellum

• Three phylogenetic divisions within the cerebellum – according to evolutionary age– The flocculonodular lobes (archicerebellum)– The anterior lobes (paleocerebellum)– The posterior lobes (neocerebellum)

Functional Division of the Cerebellum

• Three functional divisions run perpendicular to the phylogenetical divisions

• Align from the midline outwards toward the sides of the body

The Archicerebellum

• Associated with the flocculonodular lobe

• Functions– Balance (vestibular function)

• Receives input from the inferior and medial vestibular nuclei

• Sends fibers back to the vestibular nuclei • Creates a feedback loop that allows for the

constant maintenance of balance

– Eye movement

The Paleocerebellum

• Separated from the anterior lobes by the primary fissure

• Separated from the flocculonodular lobes by the posterolateral fissure

The Paleocerebellum

• Function– Controls proprioception related to muscle tone

• Receives inputs from muscle stretch receptors via the inferior olive (in the medulla)

– Send out put to the inferior cerebellar peduncle

• Receives inputs from the dorsal and ventral spinocerebellar tracts

– Carries information about the position and forces acting on the legs

– Sends axonal projections to the deep cerebellar nuclei

The Neocerebellum

• Receives input from the pontocerebellar tract– From the cerebral cortex (motor) via the pontine

nuclei in the base of the skull

• Axons project to the deep cerebellar nuclei through the middle cerebellar peduncles

• The major output tract of the cerebellum is the superior cerebellar peduncle – Sends signals to the motor cortex and the

supplementary motor area

The Neocerebellum

• Function– Control motor function

• Coordinate fine finger movements

– Feed-forward– Feed-back

Longitudinal Cerebellar Regions

• Vermis– Contributes to body posture

• Paravermal region– Regulates movements of ipsilateral

extremities (e.g. walking)

• Lateral Zone– Regulates skilled movements of ipsilateral

extremity (e.g. tying your shoe)

Deep Cerebellar nucleiDeep Cerebellar nuclei

• Dentate• Emboliform• Globose• Fastigial

Interposed

Fast G E Dent

Simplified Cerebellar Circuitry

Spinal Cord, Cerebral Cortex (via pontine nuclei), Vestibular

SystemCerebellar Cortex

Inferior OliveDeep Cerebellar Nuclei

Brainstem, thalamus, midbrain

Mossy FibersMossy Fibers

Climbing FibersClimbing Fibers

Spinal cord, Cerebral Cortex

+

-

+

INPUT

Microscopic Sections

Outer Molecular layer Stellate cells, Basket cells

Middle Purkinje cell layer Purkinje cells

Inner Granular layer Granule cells, Golgi cells

Cortex

Mol Gr

WM

PurkinjePurkinje

MolecularMolecular

GranularGranular

Major Cell Types

•Granule cells

•Purkinje cells

•Golgi cells

•Stellate cells

•Basket cells

Glutamate

GABA

GABA

GABA

GABA

***The Purkinje cell is the only output of the cerebellar cortex

5 cell types

Stellate (inhibitory)Basket (inhibitory)(molecular layer)

Purkinje (inhibitory)(Purkinje layer)

Golgi (inhibitory)Granule (excitatory)(Granular layer)

Microcircuitry of cerebellum

Inputs:

• Climbing fiber (“+”, excitatory, from inferior olive nucleus)

• Mossy fiber (+, from spinal cord & brain stem)

Output:

• Purkinje cell axon (“-”, inhibitory)

Internal circuitry A. Organization of

cortex is uniform across different subdivisions

B. AFFERENT pathways to the cerebellar cortex excite Purkinje cells.

C. Basket, stellate and Golgi cells regulate Purkinje cell activity.

D. EFFERENT pathways from the cortex originate from Purkinje cells.

Purkinje Cell

Recieves + inputs from parallel fibers and climbing fibers

Recieves - inputs from basket cells, Golgi cells, stellate cells

Heavily invested with glial processes

First direct pathway:

• climbing fiber (+) Purkinje cells (-) deep nuclei

• each climbing fiber projects to 1-10 Purkinje cells

• each Purkinje cell receives input from a single climbing fiber

• Powerful excitatory connection, each climbing fiber spike cause a burst of spikes in Purkinje cell (called a “complex spike”)

complex spike

Second direct pathway:

• Mossy fiber (+) granule cells (axon: parallel fibers, +) Purkinje cells (-) deep nuclei

• each parallel fiber projects to thousands of Purkinje cells (high divergence)

• each Purkinje cell receives input from ~200,000 parallel fibers (high convergence)

• Weak excitatory connection, spatiotemporal summation of inputs from many parallel fibers causes a single spike in Purkinje cell (called a “simple spike”)

glomeruli

simple spikes

Inhibition: focusing in time and space

•Stellate, Golgi, basket cells also receive parallel fiber input and elaborate their dendrites in the molecular layer

•Golgi cells project to granule cells

•Feed forward inhibition

•Stellate, basket cells tend to project laterally

•Collaterals of Purkinje cells also contact nearby cells

+_ _

Lateral inhibition:

• granule cells (axon: parallel fibers, +) stellate and basket cells (-) Purkinje cells in a different row

Negative feedback:

• granule cells (axon: parallel fibers, +) Golgi cells (-) granule cells

Cerebellar PedunclesCerebellar Peduncles

Superior peduncles (to the midbrain):

Fibers originate from neurons in the deep cerebellar nuclei & communicates with the motor cortex via the midbrain and the diencephalon (thalamus)

Middle peduncles (to the pons):

Cerebellum receives information advising it of voluntary motor activities initiated by motor cortex

Inferior peduncles (to the medulla):

Afferents conveying sensory information from muscle proprioceptors throughout the body & from the vestibular nuclei of the brainstem (Spinal cord)

Somatotopic Organization• Tactile information

– Ipsilateral anterior lobule – Bilateral paramedian

lobules– Cerebral Cortex and

Cerebellum have similar representations

• Motor representation– Same area as sensory

mapping– May have auditory and

visual processing

The Cerebellum

• Virtually all fibers entering and leaving the cerebellum are ipsilateral; from and to the same side of the body

Afferent ConnectionsAfferent Connections (1): (1):

1. Inferior Cerebellar Peduncle1. Inferior Cerebellar Peduncle

Restiform BodyRestiform Body Posterior Spinocerebellar TractPosterior Spinocerebellar Tract Olivocerebellar tractOlivocerebellar tract Cuneocerebellar TractCuneocerebellar Tract Reticulocerebellar TractReticulocerebellar Tract

Juxtarestiform BodyJuxtarestiform Body Vestibulocerebellar TractVestibulocerebellar Tract

Cerebellum Cerebellum ConnectionsConnections


Afferent ConnectionsAfferent Connections (2): (2):

2. Middle Cerebellar Peduncle2. Middle Cerebellar Peduncle

Pontocerebellar fiberPontocerebellar fiber Fibers from raphe nuclei Fibers from raphe nuclei

3. Superior Cerebellar Peduncle3. Superior Cerebellar Peduncle

Anterior Spinocerebellar TractAnterior Spinocerebellar Tract Tecto-cerebellar tract Tecto-cerebellar tract Trigemino-cerebellar tract Trigemino-cerebellar tract

Fibres from locus coeruleusFibres from locus coeruleus



Efferent ConnectionsEfferent Connections : :

1. Superior Cerebellar Peduncle1. Superior Cerebellar Peduncle

Cerebellothalamic fiberCerebellothalamic fiber - from 3 deep nuclei to VPLo, VLc, CL- from 3 deep nuclei to VPLo, VLc, CL Cerebellorubral fiberCerebellorubral fiber - from nucleus interpositus - from nucleus interpositus and dentate nucleusand dentate nucleus both goes to cortexboth goes to cortex Cerebello-rubro-spinal tract Cerebello-rubro-spinal tract Fibers to reticular formation and olivary complex Fibers to reticular formation and olivary complex 2. Inferior Cerebellar Peduncle2. Inferior Cerebellar Peduncle

Fastigiovestibular fiberFastigiovestibular fiber Cerebello-reticular Cerebello-reticular cerebello- olivary tract cerebello- olivary tract



Outputs of the CerebellumOutputs of the Cerebellum

Dentate nuclei: project contralaterally through the superior cerebellar peduncle to neurons in the contralateral thalamus & from thalamus to motor cortexFunc.: influence planning and initiation of voluntary movement

Emboliform & Globose nuclei: project mainly to the contralateral red nuclei & a small group is projected to the motor cortex Red Nuclei Rubrospinal Tract control of proximal limb muscles

Fastigial nuclei: project to the vestibular nuclei & to the pontine and medullary reticular formation Vestibulospinal & Reticulospinal tracts

Cerebellar nuclei: dentate, globose, emboliform, fastigial

MLFMLF

Main Connections of the VestibulocerebellumMain Connections of the VestibulocerebellumMain Connections of the VestibulocerebellumMain Connections of the Vestibulocerebellum

lower motor neuronlower motor neuron

LMNLMN

vestibulospinal tractvestibulospinal tract

FASTIGIALFASTIGIAL NUCLEUSNUCLEUS

VestibularVestibular OrganOrgan FloculonodularFloculonodular

LobeLobe

VermisVermis

ARCHICEREBELLUMARCHICEREBELLUM

VESTIBULAR NUCLEUSVESTIBULAR NUCLEUS

Main Connections of the PaleocerebellumMain Connections of the PaleocerebellumMain Connections of the PaleocerebellumMain Connections of the Paleocerebellum


SPINAL CORDSPINAL CORD

rubrospinal rubrospinal tracttract

NUCLEUSNUCLEUSINTERPOSITUSINTERPOSITUS

InferiorInferior OlivryOlivryNucleusNucleus

ANTERIOR ANTERIOR LOBELOBEPARAVERMAL PARAVERMAL ZONEZONE

PALEOCEREBELLUMPALEOCEREBELLUM

RED RED NUCLEUSNUCLEUS

spinocerebellar spinocerebellar tracttract

CEREBRALCEREBRAL CORTEXCORTEX

CEREBRALCEREBRAL CORTEXCORTEX

DENTATEDENTATENUCLEUSNUCLEUS

DENTATEDENTATENUCLEUSNUCLEUS

Main Connections of the NeocerebellumMain Connections of the NeocerebellumMain Connections of the NeocerebellumMain Connections of the Neocerebellum


LMNLMN

pyramidal pyramidal tracttract POSTERIOR POSTERIOR

LOBELOBECEREBELLARCEREBELLAR HEMISPHEREHEMISPHERE

POSTERIOR POSTERIOR LOBELOBE

CEREBELLARCEREBELLAR HEMISPHEREHEMISPHERE

THALAMUSTHALAMUSTHALAMUSTHALAMUS

NEOCEREBELLUMNEOCEREBELLUM

PontinePontineNucleusNucleusPontinePontineNucleusNucleus

upper motor neuronupper motor neuron

UMNUMN

upper motor neuronupper motor neuron

UMNUMN

BASALBASALGANGLIAGANGLIABASALBASAL

GANGLIAGANGLIA

Pyramidal Tract and Associated CircuitsPyramidal Tract and Associated CircuitsPyramidal Tract and Associated CircuitsPyramidal Tract and Associated Circuits


UMNUMN


UMNUMN

pyramidal tractpyramidal tract

CerebellumCerebellumCerebellumCerebellum

ReticularFormation

ReticularFormation

CEREBELLUMCEREBELLUM

Cerebellum and Automatic Motor ControlCerebellum and Automatic Motor ControlCerebellum and Automatic Motor ControlCerebellum and Automatic Motor Control

Lower Motor Neuron (LMN)Lower Motor Neuron (LMN)Lower Motor Neuron (LMN)Lower Motor Neuron (LMN)

Motor CortexMotor Cortex

Red NucleusRed Nucleus

Vestibular Nucleus

Vestibular Nucleus

ProprioceptorsProprioceptorsProprioceptorsProprioceptors

Olivocerebellar ConnectionsOlivocerebellar Connections

Caudal portion ofCaudal portion of medial and dorsal accessory olivary nucleusmedial and dorsal accessory olivary nucleus ----------------- vermis of cerebellar cortex (A and B)----------------- vermis of cerebellar cortex (A and B) fastigial nucleusfastigial nucleus vestibular nucleusvestibular nucleus

Rostral portion ofRostral portion of medial and dorsal accessory olivary nucleusmedial and dorsal accessory olivary nucleus ----------------- paravermal region (C----------------- paravermal region (C11, C, C22, C, C33)) nucleus interpositusnucleus interpositus

Principal Inferior Olivary NucleusPrincipal Inferior Olivary Nucleus

----------------- cerebellar hemisphere (D----------------- cerebellar hemisphere (D11, D, D22)) dentate nucleusdentate nucleus



CerebellumCerebellum FunctionFunction

CerebellumCerebellum FunctionFunction

Maintenance of EquilibriumMaintenance of Equilibrium - balance, posture, eye movement - balance, posture, eye movement

Coordination of half-automatic movement ofCoordination of half-automatic movement of walking and posture maintenancewalking and posture maintenance - posture, gait - posture, gait

Adjustment of Muscle ToneAdjustment of Muscle Tone

Motor Learning – Motor SkillsMotor Learning – Motor Skills

Cognitive FunctionCognitive Function

Cerebellum: Control of Voluntary MovementCerebellum: Control of Voluntary MovementAll three lobes of cerebellum work together- Comparator of a servo-mechanism All three lobes of cerebellum work together- Comparator of a servo-mechanism

Primary function: 1. To supplement & correlate the activities of other motor areas2. Control of posture 3. Correction of rapid movements initiated by cerebral cortex4. Motor learning

Frequency of nerve impulses in the climbing fibers almost doubles when a monkey learns a new task

Movement Control:a. Inputs from motor cortex inform the cerebellum of an intended

movement before it is initiatedb. Sensory information is then received via the

spinocerebellar tractc. An error signal is generated and is fed back to the cortex

Cerebellum and Motor LearningCerebellum and Motor Learning• Deficits in learning complex motor tasks after

cerebellar lesions• fMRI studies : cerebellum active during learning

of novel movements• Postulated that cerebellar nuclei store certain

motor memories• May be involved in cognitive functionsCerebellar Cognitive FunctionCerebellar Cognitive Function• Plays a role in language and problem solvingPlays a role in language and problem solving• Recognizes and predicts sequences of eventsRecognizes and predicts sequences of events

Cerebellar Processing - 1• The frontal motor association areas of the

cerebral cortex indicates its intents to initiate voluntary muscle contractions

• Through collateral fibers of the pyramdial tracts, it notifies the cerebellum of its activity

Cerebellar Processing - 2• At the same time, the cerebellum receives

information from the proprioceptors throughout the body – Tension in muscles, tendons, and joint positions– From visual and equilibrium pathways

• This information enables the cerebellum to determine where the body is and where it is going – More specifically where the parts of the body

are located in space and how are they moving

Cerebellar Processing - 3• The cerebellar cortex assesses this

information and calculates the best way to coordinate the force, direction, and extent of muscle contraction– Prevents overshoot– Maintains posture– Ensures smooth, coordinated movements

Cerebellar Processing - 4• Via the superior peduncles, the cerebellum

dispatches its “blueprint” for coordination to the cerebral motor cortex which makes appropriate adjustments in its motor plan

• Cerebellar fibers also flow to brain stem nuclei, such as the red nuclei of the midbrain, which in turn project to motor neurons of the spinal cord

The Cerebellum

• The cerebellum continually compares the higher brain’s intention with the body’s performance and sends out messages to initiate the appropriate measures

• In this way, it helps to promote smooth voluntary movements that are precise and economical in terms of muscular effort

The Cerebellum

• Cerebellar injury results in the loss of muscle tone and clumsy, unsure movements, and sometimes even impaired thoughts about movements

Clinical Considerations• Signs of Dysfunction

– Impaired Muscle Synergy– Reduced Muscle Tone– Evident in Skilled Tasks– Nystagmus – Ataxia : incoordination of movement

- decomposition of movement - dysmetria, past-pointing

- dysdiadochokinesia - gait ataxia, truncal ataxia

• Slow Movement (Bradykinesia)• Mild Muscular Weakness (Asthenia)• Asynergia• Speech difficulties (Ataxic Dysarthria)

– affects respiration, phonation, resonance and articulation, but most pronounced in articulation and prosody.

Clinical Considerations 2

• Dysdiadochokinesia– Clumsiness in Alternating Movements– Tapping, Speech Sound

• Dysarthria– Ataxic Dysarthria– Scanning Speech – Slurred and Disjointed Speech

• Dysmetria– Error in Judgment of Range and Distance of Target– Undershooting or Overshooting

Clinical Considerations 3

• Intentional Tremor– Accessory Movement During Volitional Task– vs. Parkinson’s Disease Where Tremor Lessens

During Volitional Movement

• Hypotonia– Reduced Resistance to Passive Stretch

• Rebounding– Inability to Predict Movement – Cannot Hold Back Movement

• Disequilibrium– Unsteady Gait, Body Wavering

Cerebellar Pathologies

• Cerebrovascular Accident (CVA)– Thrombotic, embolic or hemorrhagic– Vertebrobasilar Artery

• Toxicity– Chronic Alcoholism

• Progressive Cerebellar Degeneration– Friedrich's Ataxia: Autosomal Recessive

Heredity Degenerative Condition– Combined Sensory and Motor Dysfunctions

PosturePostureGait – AtaxiaGait – Ataxia

TremorTremor

Cerebellar Cerebellar AtaxiaAtaxia

Ataxic gait and Ataxic gait and position: position: Left cerebellar tumorLeft cerebellar tumor

a. Sways to the right ina. Sways to the right in standing positionstanding position

b. Steady on the b. Steady on the right legright leg

c. Unsteady on the c. Unsteady on the left legleft leg

d. ataxic gaitd. ataxic gait

a b c

d

Cerebellar tumors on Cerebellar tumors on vermisvermis

- Truncal Ataxia- Truncal Ataxia

- Frequent Falling- Frequent Falling

The child in this picture:The child in this picture:

- would not try to stand - would not try to stand unsupportedunsupported

- would not let go of the bed - would not let go of the bed

railrail if she was stood on the floor.if she was stood on the floor.

Cerebellar Cerebellar MedulloblastomaMedulloblastoma

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